1. Field of the Invention
The present invention relates generally to substrate and semiconductor wafer preparation systems and methods, and more particularly, the present invention relates to the cleaning and drying of substrates and semiconductor wafers implementing a surface tension reducing process and employing space and process efficient systems.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform wet cleaning of substrates at various stages of the fabrication process. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed over and into silicon substrates. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. At each metallization level there is a need to planarize metal or associated dielectric material. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to the higher variations in the surface topography. In some applications, metallization line patterns are formed in the dielectric material, and then metal CMP operations are performed to remove excess metallization.
Following each CMP operation, a wet clean of the substrate is performed. The wet clean is designed to wash away any by-products of the fabrication process, remove contaminants, and to achieve and maintain the necessary degree of cleanliness essential to proceed to a subsequent fabrication operation. As transistor device structures become smaller and more complex, the precision required to achieve and maintain structure definition demands exacting standards of cleanliness be maintained in all process operations. If a wet clean is incomplete or ineffective, or if a post-wet clean drying is incomplete or ineffective, then unacceptable residue or contaminants are introduced into the processing environment.
Similarly, in the fabrication of hard disk drives, planarization and cleaning operations are needed to maintain a clean and smooth disk substrate. Residue or contaminants remaining on substrates in the fabrication of hard disks and other devices utilizing similar substrates is likewise unacceptable.
Rinsing and drying techniques, methods, and apparatus are plentiful and known in the art, and incorporate such operations as rinsing and scrubbing, immersion, and the application of thermal, mechanical, chemical, electrical, or sonic energy and the like to remove or displace water and dry the substrate. While some scrub and rinse operations may employ acids or bases for vigorous interaction with fabrication by-products, deionized water (DIW) is commonly used to perform a final rinse before the desired drying technique is performed.
One common drying technique is known as spin, rinse and dry (SRD). SRD uses mechanical, centrifugal, energy to rid the substrate of water by spinning the substrate until dry. An SRD apparatus typically includes a substrate mounting plate within a bowl and mounted on a shaft that is configured to rotate and thus spin the substrate. The substrate is typically attached to the substrate mounting plate or spin chuck with mounting pins configured to maintain the substrate in a horizontal orientation. Rapid rotation of the spin chuck therefore spins the substrate and forces the water from the surface of the substrate. DIW is typically dispensed from a nozzle which is positioned over the substrate and connected to a DIW supply.
The SRD process essentially includes applying DIW and spinning the substrate dry. The drying can be enhanced with the introduction of an inert gas such as Nitrogen or an inert gas vapor to displace any water that is not completely removed by spinning. Additional variations include heating the DIW, heating the SRD environment, heating the inert gas, and the like.
Another common drying technique is known as a Marangoni technique. Marangoni drying typically includes using a chemical drying fluid or solvent such as isopropyl alcohol (IPA) to introduce favorable surface tension gradients facilitating removal of water from the surface of a substrate. Variations of the Marangoni technique also include the introduction of an inert gas such as Nitrogen as a carrier gas for IPA vapor delivery.
Prior art drying also includes the combination of the Marangoni technique with an SRD apparatus. This method has included the introduction of IPA or IPA vapor to a surface of a substrate which is mounted on a spin chuck. As the spin chuck rotates the substrate, centrifugal force drives water from the surface of the substrate, and Marangoni drying maximizes removal of water from the surface of the substrate while minimizing residue or contaminants.
A limitation of the combination of SRD and Marangoni techniques is that the typical prior art SRD provides for single-sided rinsing and drying of a wafer or substrate. A substrate mounted on a spin chuck has only one surface exposed for rinsing and drying. In order to achieve and maintain the level of cleanliness desired for current fabrication environments, simultaneous dual-sided rinsing and drying is needed.
In view of the foregoing, there is a need for substrate preparation systems and methods that maximize the cleaning and drying of wafers and other substrates in order to meet and exceed the ever more stringent cleanliness requirements for fabrication processes.